1. Field of the Invention
The present invention relates to an optical disc inclination detecting method, an optical pickup device, and an optical disc device, and is applicable to detection of inclination of a disc when recording or reproducing information recorded on a disk-shaped recording medium, such as a magneto-optical disc (MO), a compact disc (CD), a compact disc-recordable (CD-R), and a digital video disc (DVD).
2. Description of the Related Art
In the field of optical discs, recently, in additional to the conventional CD format, optical discs of various formats are present, including the optical disc-recordable (CD-R) coated with a pigment film of organic pigment system, magneto-optical disc (MO), phase variable optical disc (DVD-RAM) and the like.
In the recording and reproducing apparatus of such optical discs, it is designed to control the radial tilt angle indicating the inclination of the optical disc in the radial direction with respect to the light spot emitted from the optical pickup. As the recording density is enhanced, it is required much to detect the radial tilt of the optical disc precisely and assure the reliability by radial tilt control of optical disc.
In such optical disc recording and reproducing apparatus, when detecting the radial tilt of optical disc, a tilt sensor having a reflection type sensor is mounted, for example, on the optical pickup, and the radial tilt is detected from the difference in the quantity of reflected light when the optical pickup is moved in the radial direction of the optical disc.
Japanese Laid-open Patent No. 8-255360 disclosed an optical disc device capable of removing a DC offset by detecting the reflected light from the optical disc with two photo detectors, generating a differential signal, detecting the envelope of the detection signal to detect the differential component, and further controlling the tracking from their difference.
Japanese Laid-open Patent No. 9-212891 discloses an optical head device for dividing the laser light into a main luminous flux and a subsidiary luminous flux, generating rush-pull signals individually from them, and generating a tilt signal corresponding to the disc tilt from these push-pull signals. Also, japanese Laid-open Patent No. 9-245357 discloses a servo control device of an optical disc recording and reproducing apparatus for converting from a push-pull signal and a phase difference detection signal into a detracking signal and a radial tilt signal, to thereby controlling the tracking servo and the sled servo.
In the optical disc recording and reproducing apparatus using such conventional tilt sensor, since the optical pickup and the tilt sensor cannot be placed at the same position in the optical disc radial direction, the position in the optical disc radial direction detected by the tilt sensor and the focal position of the optical pickup are different, and a correct tilt angle of the disc with respect to the optical pickup cannot be obtained. Besides, since the tilt sensor is mounted on the optical pickup, the optical pickup is increased in size.
In Japanese Laid-open Patent No. 8-255360, in order to remove the DC offset components, since it was necessary to adjust the balance by fine adjustment of the gain when subtracting the push-pull signal of one beam, the adjustment was complicated, and the precision was lowered unless the adjustment was appropriate. In Japanese Laid-open Patent No. 9-212891, since the gain was adjusted after assuming up the two push-pull signals of the subsidiary luminous flux and the offset signal was generated by adding it to the push-pull signals of the main luminous flux, the gain adjustment was complicated, and the precision was lowered unless the adjustment was appropriate. In Japanese Laid-open Patent No. 9-245357, since the radial tilt signal was converted by amplifying the push-pull signal and the phase difference detection signal of one beam to specified levels respectively, the gain adjustment was complicated, and the precision was lowered unless the adjustment was appropriate.
The present invention is devised in the view of the aforesaid problems, and it is hence an object thereof to present an optical disc inclination detecting method, an optical pickup device, and an optical disc device capable of detecting the radial tilt of optical disc at high precision by a simple constitution.
To solve the problems, the optical disc inclination detecting method of the present invention is an optical disc inclination detecting method for detecting the inclination angle of an optical disc with respect to a light spot, for recording information or reproducing information by irradiating the light spot on an optical disc by an optical pickup, comprising the steps of dividing the light spot into a main spot and both side spots on a specified track and track crossing directions before and after the same, generating, from the reflected light from the optical disc, a first signal by subtracting or adding the detection signals from split photo detectors or light receiving units of the main spot and both side spots or in the track crossing direction of both side spots generating a second signal by comparing the phase of the detection signals from the split photo detectors in the direction orthogonal to the track crossing direction of the main spot, determining a differential operation value of the first signal and the second signal, and detecting the inclination angle of the optical disc on the basis of the differential operation value.
The optical pickup device of the invention is an optical pickup device for detecting the inclination angle of an optical disc with respect to a light spot, for recording information or reproducing information by irradiating the laser spot on the optical disc, comprising an inclination angle detecting unit in which the light spot is divided into a main spot and both side spots in a specified track and in the track crossing direction before and after the same, a first signal is generated from the reflected light from the optical disc by subtracting or adding the detection signals from split photo detectors of the main spot and both side spots or in the track crossing direction of both side spots, a second signal is generated by comparing the phases of the detection signals from the split photo detectors or light receiving units in the direction orthogonal to the track crossing direction of the main spot, a differential operation value of the first signal and the second signal is determined, and the inclination angle of the optical disc is detected on the basis of the differential operation value, and a correcting unit which corrects the inclination angle of the optical disc with respect to the light spot depending on the inclination angle.
Further, the optical disc device of the invention is an optical disc device for detecting the inclination angle of an optical disc with respect to a light spot, for recording information or reproducing information by irradiating the laser spot on the optical disc by an optical pickup, comprising an inclination angle detecting unit in which the light spot is divided into a main spot and both side spots in a specified track and in the track crossing direction before and after the same, a first signal is detected from the reflected light from the optical disc by subtracting or adding the detection signals from split photo detectors or light receiving units of the main spot and both side spots or in the track crossing direction of both side spots, a second signal is generated by comparing the phases of the detection signals from the split photo detectors in the direction orthogonal to the track crossing direction of the main spot, a differential operation value of the first signal and the second signal is determined, and the inclination angle of the optical disc is detected on the basis of the differential operation value, and a correcting unit which corrects the inclination angle of the optical disc with respect to the light spot depending on the inclination angle.
The optical disc device of the invention brings about the following actions.
The laser beam emitted from an optical pickup of an optical system is irradiated on an optical disc which is controlled in rotation by a spindle servo system. Focus servo is effected by a focusing coil of a biaxial actuator of the optical system which is controlled by a focus servo system, and also tracking servo is effected by a tracking coil of the biaxial actuator.
The reflected light from the optical disc is detected by split photo detectors or light receiving units of a servo signal detecting system, a first signal and a second signal are generated by using detection signals from the split photo detectors, and the difference between the first signal and the second signal is calculated to determine the inclination angle of the disc. The detected disc inclination angle is corrected by a correction unit.